1. Field of the Invention
The present invention relates to a seat-height adjusting device.
2. Description of the Prior Art
In Japanese Patent Laid-open Print No. 63(1988)-90452 published in Apr. 21, 1988 without examination, a conventional seat-height adjusting device is disclosed. The conventional seat-height adjusting device includes a first gear having an inner teeth portion and secured to a seat-cushion with, and a second gear having an outer teeth portion and pivoted to a vehicle-floor side. The outer teeth portion is in meshing engagement with the inner teeth portion and is less than the inner teeth portion in teeth number. A shaft is rotatably mounted to the vehicle-floor side, and has an eccentric portion for supporting the second gear. When the shaft is rotated, the outer teeth portion of the second gear is brought into cycloid movement along the inner teeth portion of the first gear, which results in the inclination of the second gear. Thus, the height of the seat-cushion is expected to be varied relative to the vehicle-floor side.
In the foregoing structure, whenever one rotation of the shaft is established, the second gear moves inwardly in the radial direction temporarily due to the direct engagement of the inner and outer teeth portions, and the cycloid movement of the outer teeth portion of the second gear is not smooth as a whole. Thus, this cause an unnatural movement of the seat-cushion, which leads to an occupant's discomfort. In addition, the backlash between the inner and outer teeth portions which serves for smooth engagement therebetween may sometimes becomes play or rattle. This also will bring the occupant's discomfort.
The former drawback can be overcome by avoiding the direct engagement of the inner and outer teeth portions which is suggested by Japanese Patent Publication No. 56(1981)-14890 corresponding to U.S. Pat. No. 4,143,912. That is to say, a seat-reclining device disclosed in this reference includes a shaft having two true round portions and an eccentric portion therebetween, a stationary gear having an inner teeth portion and mounted on one of the true round portion, a movable member having an inner teeth portion and mounted on the other of the true round portion, an intermediate gear mounted on the eccentric portion and having an outer teeth portion which is in meshing engagement with both of the inner teeth portions of the stationary and movable gears. The inner teeth portions and the outer teeth portion differ each other in teeth number. In this structure, the intermediate gear prevents the radial movement of the movable gear.
The latter drawback can be overcome by the suggestion of Japanese Patent Laid-open Print No. 62(57517) corresponding to U.S. Pat. No. 4,708,392. This reference shows that a tapered eccentric portion of the shaft will establish an easy adjustment of the engagement between inner and other teeth portions by moving the shaft in the axial direction.
However, concurrently overcoming both of the foregoing drawbacks can not be attained by the combination of the foregoing two concepts. The reason is that in Japanese Patent Publication No. 56(1981)-14890 corresponding to U.S. Pat. No. 4,143,912 the shaft does not move in the axial direction since the eccentric portion is held between the the movable and stationary gears.